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- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-URI http://asc.fasb.org/extlink&oid=73531372&loc=d3e2207-128464

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 1
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44278-110382

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500269&loc=d3e45485-110386

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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Period end amount of construction work in progress in public utility.

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- Definition

Period end book value of other property, plant and equipment (PPE) owned (but not classified elsewhere) by the public utility.

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No definition available.

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Property, Plant and Equipment (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) MW	Jun. 30, 2016 USD ($)	Apr. 30, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 10.1	$ 15.3	$ 27.1	$ 28.5
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	6.1	12.1	20.4	22.4
Estimated fair value of net assets acquired					$ 32.0
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	4.0	$ 3.2	$ 6.7	$ 6.1
Marshalltown Generating Station [Member] \| IPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW			660
Marshalltown Generating Station [Member] \| Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Total project costs	640.0		$ 640.0
Allowance for funds used during construction			$ 81.0
West Riverside Energy Center [Member] \| WPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) \| MW			730
West Riverside Energy Center [Member] \| Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 185.0		$ 185.0
Allowance for funds used during construction			$ 5.0